A typical example of the electronic stringed musical instrument is disclosed in Japanese Patent Application laid-open ( Kokai ) No. 62-99790. In the electronic stringed musical instrument, super-sonic vibrations are periodically supplied from piezo electric transducers to strings, respectively, for deciding fret positions each assigned a fret member contacted with each of the strings, and each of the fret position is decided on the basis of a time interval measured from the production of a supersonic vibration to the receipt of an echo of the super-sonic vibration reflected from the fret member. When the fret positions are thus decided, the electronic stringed musical instrument is ready for the production of sounds. Upon detection of a plucking motion, the electronic musical instrument produces a sound with the particular note assigned to the fret position decided in the previous stage.
However, a problem is encountered in the electronic stringed musical instrument disclosed in the Japanese Patent Application laid-open in the credibility of the fret position decided on the basis of the time interval for which the super-sonic vibration travels. Namely, the prior-art electronic stringed musical instrument decides the fret position on the assumption that a distances between each piezo electric transducer and the respective fret members are unchangeable throughout the service life of the electronic stringed musical instrument. However, the distances tend to be varied within a relatively short time period due to a deformation of a neck portion where the fret members are embedded. Such a deformation takes place due to, for example, variations of the tension applied to each of the strings. Moreover, when each of the strings is lengthened, the time interval is also varied for every fret member. Another reason for an error made in the decision of the fret position is that the string is liable to transiently brought into contact with another fret member during a low frequency vibration produced by the plucking motion. If the string comes in contact with another fret member, the super-sonic vibration merely travels a shortened path in the string, and, accordingly, the time interval is fallen within a range established for another fret, thereby causing the electronic stringed musical instrument to make an error in the decision of the fret position. Noise vibrations further cause the electronic stringed musical instrument to make an error in the decision of the fret position, because the piezo electric transducer converts not only the echo of the super-sonic vibration reflected from the fret but also noise vibrations produced upon reflection from, for example, a tailpiece where the string is anchored into an electric signal.
The prior-art electronic stringed musical instrument further has a problem in the detection of the plucking motion. When the string is strongly plucked by the player, a low frequency vibration with a wide amplitude takes place in the string. The low frequency vibration is converted into an electric signal similar in waveform to the low frequency vibration, and the electronic stringed musical instrument detects the plucking motion when the amplitude of the electric signal excesses a predetermined threshold value. However, if the player repeats the plucking motion which results in a low frequency vibration with an extremely wide amplitude, the amplitude of the electric signal continues to remain over the predetermined threshold value, and, for this reason, the electronic stringed musical instrument looses the production timings for the latter plucking motions.
Still another problem is encountered in the prior art electronic stringed musical instrument in the variety of a musical playing technique. The electronic stringed musical instrument disclosed in the Japanese Patent Application laid-open does not take into account of various musical playing techniques such as, for example, a bent-string playing technique, a "legato" technique or a muting technique. Then, the musical expression is limited to a narrow range.